The development of a dissolved radon calibration source for nexo, updating the electronic recoil model in nest, and recommendations for the integration of diversity, equity, and inclusion work into physics

McMichael, Kirsten, Deidre
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Giedt, Joel
Liu, Emily
Wertz, Esther
Brown, Ethan
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This dissertation presents three main projects - the development of a radon injection chamberfor nEXO, the implementation of an updated yields and recombination model for the Noble Element Simulation Technique (NEST), and recommendations for the integration of diversity, equity, and inclusion (DEI) work into physics. nEXO is a next generation tonne-scale liquid xenon time projection chamber that is designed to observe neutrinoless double beta decay (0νββ). If observed, this would confirm that the neutrino is Majorana in nature (meaning it is its own antiparticle), lead to a plethora of beyond standard model physics, and provide insight into the matter-antimatter asymmetry of the universe. To observe such a rare event, nEXO must achieve an energy resolution of < 1% at the Q-value of 0νββ decay. This can only be done if the light response is known throughout the detector via the creation of a lightmap using calibration sources. However, as detectors reach the tonne-scale and beyond this task is no longer trivial as typical calibration sources such as external gammas are no longer able to penetrate the detector center. To resolve this issue, this work presents the development of a radon injection chamber that uses radon-220 as an internal calibration source. The setup detailed in Chapter 3 allows for the study of radon-220 and its daughters as they flow through xenon and based on the results produced from the test stand recommendations will be made to nEXO to inform the calibration scheme. The work presented in this chapter demonstrates the capability of the RPI test stand infrastructure to run a variety of scintillation detection experiments. Presented is the completion and characterization of a liquid noble cryogenic system, demonstrated temperature and pressure control consistent with the needs of high purity liquid noble experiments, measurements of the cooling power capacity of the system, and argon liquifaction as a proxy for the safe handling of xenon in the system. Additionally, a successful small-scale method was developed for coating materials with TPB and shifting wavelengths from 128nm to 450nm. An external argon gas chamber was also built to detect light signals from alpha events and validate the effectiveness of the TPB coatings in an actual detector. Combining the resulting components of these two tests will now allow for a full scale radon injection run to be done with argon and then eventually with xenon. Complementary to the experimental work presented, Chapter 4 details simulation work via the implementation of an updated yields and recombination model for NEST. NEST is a C++ package with optional GEANT4 integration and a Python equivalent (nestpy) that accurately simulates the scintillation, ionization, and electroluminescence processes in xenon and argon. Using a combination of empirical and first principle methods, NEST models the intrinsic physics of noble detectors such as LUX and XENON1T. While NEST has an impressive track record for successfully simulating most experiments, it saw a 25% disagreement in the yields when compared to the results of nEXO’s predecessor EXO-200. This disagreement stems from EXO-200 measuring a W-value of 11.5 eV which is significantly lower than the standard value in the model of 13.7 eV. For the purpose of this work, the Wvalue is defined as the average amount of energy required to produce a quantum of charge or light and therefore has a direct impact on the yields. To correct this discrepancy, the modified Thomas Imel Box (TIB) Model has been implemented into NEST and parameters were constrained using a variety of real world data. The resulting model shows good agreement with a wide range of data for both low and high energies and fields, making the new modified TIB model a promising path forward for NEST. In the final chapter, recommendations for the integration of diversity, equity, and inclusion work into physics are presented. Specifically assessed is the current status of DEI in the field, case studies of ongoing DEI efforts at the local (department) level and large-scale (international scientific collaboration) level, and finally best practices and recommendations for integrating DEI into physics is discussed. This work mainly focuses on DEI committees and their impact and role in physics organizations, however additional work such as the creation of a community of practice is laid out.
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